balanced cables FREE cabling and networking Helpdesk
 Question by ali jaber posted 02 Aug 2007
 balanced cables
Dear Sir/Madam
If a 75 ohm coaxial cable has 1.8mm wire diameter and solid Polyethylene Insulation Material and can achieve 1.3dBs max at 200KHz, what is the equivalent balanced 75 ohm "2 insulated wires" cable which can achieve such attenuation figures. The 2 insulated wires twisted together and will be then surrounded by a tinned wire braid. I need to know the wire diameter in each. Is there a relationship between the wire size in the coaxial and the wire size in the 2 insulated core design?

Many kind regards
Ali Jaber
 Answer by Dmitri Abaimov posted 02 Aug 2007
Dear Ali,

I would not be able to answer such detailed question as none of us here is trained in cabling physics to the degree needed to properly address the issue. We see our mission here as answering questions related to designing, installing and testing cabling systems, not designing the actual individual components of those.

Also, please note that you did not provide the length of the cable needed. In fact, you can create a situation where a pair from a standard CAT5E cable (100 Ohm) will have the attenuation required, depending on how far you need to go. You would then have to provide a device, such as a transformer, to match the impedances of the cable and the rest of your circuit.

But, to answer your qualitative question about the size, the size absolutely matters here (both the wires and the surrounding insulation) because it affects capacitance between the conductors or the conductor and the shield around it.

Dmitri Abaimov, RCDD

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